1. Field of the Invention
This invention relates in general to communications systems, and in particular a low-cost multi-mission broadband communications payload.
2. Description of Related Art
Communications satellites have become commonplace for use in many types of communications services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, satellites must provide signals to various geographic locations on the Earth""s surface. As such, typical satellites use customized antenna designs to provide signal coverage for a particular country or geographic area.
Many satellite payloads contain analog or digital signal processors. Analog processors are typically used to separate and combine different signals into specific channels (xe2x80x9cchannelize the signalsxe2x80x9d), and to switch different parts of the ground-to-satellite (xe2x80x9cuplinkxe2x80x9d) signal to different satellite-to-ground (xe2x80x9cdownlinkxe2x80x9d) beams. Digital processors are also used to channelize and switch signals, and may also be used to demodulate, process and remodulate signals. Usually these signal processors are heavy and consume a lot of DC power, so it is advantageous to be as efficient as possible in allocating processing resources to uplink beams.
Further, the signals (xe2x80x9ctrafficxe2x80x9d) in each uplink beam to the satellite are different, since the population and economy in each uplink region is different. If the amount of traffic in each uplink beam is known before the satellite is launched, and does not vary over the life of the satellite, processing resources can be allocated to uplink beams with fixed connections, which eliminates the need for the switch matrix. Typically, however, the amount of traffic in each uplink beam is either unknown beforehand or varies over time, and thus there must be some sort of switch matrix to reallocate and interconnect uplink beams to the on-board satellite processing resources. Similar traffic changes occur in downlink beams, with similar problems for the satellite and associated infrastructure to support users on the ground.
Communications satellites are operated in various modes. Some satellites operate as simple repeaters, typically known as a xe2x80x9cbent-pipexe2x80x9d configuration, where the uplink signal is merely repeated, at a different frequency, in a downlink signal. No processor capability is available onboard the satellite other than frequency translation between the uplink and downlink signals, and, if necessary, amplification of the downlink signal to allow ground based receivers to receive the signal.
Multi-beam satellites were introduced to allow the satellite to receive signals from multiple sources and relay those signals to multiple destinations and take advantage of frequency reuse to increase system capability. In a multi-beam satellite, however, the ability of the satellite to relay a given uplink signal to a desired downlink destination was still limited.
To help to reduce this limitation, multi-beam satellites that have on-board switching capability have been deployed. These satellites receive an incoming beam containing several frequency-multiplexed channels, demultiplex (demux) the signal on-board the satellite, and inter-beam switch these channels into a desired downlink beam.
Satellite based broadband communications networks rely on highly efficient and flexible payloads which act as virtual nodes within the network. The satellite""s payload provides connectivity among the network of user terminals on the ground and other satellites in the constellation, as well as the central network operations center. This connectivity allows data links to be established between any two points on the earth.
It can be seen, then, that there is a need in the art for a communications system that can support multiple missions without the need for redesigning the entire system. It can also be seen that there is a need in the art for a communications system that can be programmed in flight to accommodate the changing needs of uplink and downlink traffic.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and system for communicating using satellites. The system comprises a receive system, a downlink system, and a data processing system. The receive system receives an uplink signal comprising at least one data packet from at least one user in an uplink cell. The ground programmable downlink system transmits the data packet to a specific downlink cell and adjusts a power used to transmit the data packet to the specific downlink cell. The ground programmable data processing system processes and routes the data packet to an input of the downlink system such that the downlink system transmits the data packet to the specified downlink cell.
The method comprises receiving at the satellite an uplink signal comprising at least one data packet from at least one user in an uplink cell, processing the data packet on the satellite, routing the data packet to a transmit antenna on the satellite, adjusting a power level of a transmitter used to transmit the data packet from the satellite to a specific downlink cell, and transmitting the data packet to the specified downlink cell.
The present invention provides a communications system that can support multiple missions without the need for redesigning the entire system. The present invention also provides a communications system that can be programmed in flight to accommodate the changing needs of uplink and downlink traffic.